Message-ID: <8ce2cd7b-7702-45aa-b4c8-25a01c27ed83@arm.com>
Date: Fri, 9 Feb 2024 13:44:20 +0000
From: Robin Murphy <robin.murphy@....com>
To: Pasha Tatashin <pasha.tatashin@...een.com>, akpm@...ux-foundation.org,
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Subject: Re: [PATCH v4 01/10] iommu/vt-d: add wrapper functions for page
 allocations

On 2024-02-07 5:40 pm, Pasha Tatashin wrote:
[...]> diff --git a/drivers/iommu/iommu-pages.h 
b/drivers/iommu/iommu-pages.h
> new file mode 100644
> index 000000000000..c412d0aaa399
> --- /dev/null
> +++ b/drivers/iommu/iommu-pages.h
> @@ -0,0 +1,204 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2024, Google LLC.
> + * Pasha Tatashin <pasha.tatashin@...een.com>
> + */
> +
> +#ifndef __IOMMU_PAGES_H
> +#define __IOMMU_PAGES_H
> +
> +#include <linux/vmstat.h>
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +
> +/*
> + * All page allocation that are performed in the IOMMU subsystem must use one of

"All page allocations" is too broad; As before, this is only about 
pagetable allocations, or I guess for the full nuance, allocations of 
pagetables and other per-iommu_domain configuration structures which are 
reasonable to report as "pagetables" to userspace.

> + * the functions below.  This is necessary for the proper accounting as IOMMU
> + * state can be rather large, i.e. multiple gigabytes in size.
> + */
> +
> +/**
> + * __iommu_alloc_pages_node - allocate a zeroed page of a given order from
> + * specific NUMA node.
> + * @nid: memory NUMA node id
> + * @gfp: buddy allocator flags
> + * @order: page order
> + *
> + * returns the head struct page of the allocated page.
> + */
> +static inline struct page *__iommu_alloc_pages_node(int nid, gfp_t gfp,
> +						    int order)
> +{
> +	struct page *page;
> +
> +	page = alloc_pages_node(nid, gfp | __GFP_ZERO, order);
> +	if (unlikely(!page))
> +		return NULL;
> +
> +	return page;
> +}

All 3 invocations of this only use the returned struct page to trivially 
derive page_address(), so we really don't need it; just clean up these 
callsites a bit more.

> +
> +/**
> + * __iommu_alloc_pages - allocate a zeroed page of a given order.
> + * @gfp: buddy allocator flags
> + * @order: page order
> + *
> + * returns the head struct page of the allocated page.
> + */
> +static inline struct page *__iommu_alloc_pages(gfp_t gfp, int order)
> +{
> +	struct page *page;
> +
> +	page = alloc_pages(gfp | __GFP_ZERO, order);
> +	if (unlikely(!page))
> +		return NULL;
> +
> +	return page;
> +}

Same for the single invocation of this one.

> +
> +/**
> + * __iommu_alloc_page_node - allocate a zeroed page at specific NUMA node.
> + * @nid: memory NUMA node id
> + * @gfp: buddy allocator flags
> + *
> + * returns the struct page of the allocated page.
> + */
> +static inline struct page *__iommu_alloc_page_node(int nid, gfp_t gfp)
> +{
> +	return __iommu_alloc_pages_node(nid, gfp, 0);
> +}

There are no users of this at all.

> +
> +/**
> + * __iommu_alloc_page - allocate a zeroed page
> + * @gfp: buddy allocator flags
> + *
> + * returns the struct page of the allocated page.
> + */
> +static inline struct page *__iommu_alloc_page(gfp_t gfp)
> +{
> +	return __iommu_alloc_pages(gfp, 0);
> +}
> +
> +/**
> + * __iommu_free_pages - free page of a given order
> + * @page: head struct page of the page
> + * @order: page order
> + */
> +static inline void __iommu_free_pages(struct page *page, int order)
> +{
> +	if (!page)
> +		return;
> +
> +	__free_pages(page, order);
> +}
> +
> +/**
> + * __iommu_free_page - free page
> + * @page: struct page of the page
> + */
> +static inline void __iommu_free_page(struct page *page)
> +{
> +	__iommu_free_pages(page, 0);
> +}

Beyond one more trivial Intel cleanup for __iommu_alloc_pages(), these 3 
are then only used by tegra-smmu, so honestly I'd be inclined to just 
open-code there page_address()/virt_to_page() conversions as appropriate 
there (once again I think the whole thing could in fact be refactored to 
not use struct pages at all because all it's ever ultimately doing with 
them is page_address(), but that would be a bigger job so definitely 
out-of-scope for this series).

> +
> +/**
> + * iommu_alloc_pages_node - allocate a zeroed page of a given order from
> + * specific NUMA node.
> + * @nid: memory NUMA node id
> + * @gfp: buddy allocator flags
> + * @order: page order
> + *
> + * returns the virtual address of the allocated page
> + */
> +static inline void *iommu_alloc_pages_node(int nid, gfp_t gfp, int order)
> +{
> +	struct page *page = __iommu_alloc_pages_node(nid, gfp, order);
> +
> +	if (unlikely(!page))
> +		return NULL;

As a general point I'd prefer to fold these checks into the accounting 
function itself rather than repeat them all over.

> +
> +	return page_address(page);
> +}
> +
> +/**
> + * iommu_alloc_pages - allocate a zeroed page of a given order
> + * @gfp: buddy allocator flags
> + * @order: page order
> + *
> + * returns the virtual address of the allocated page
> + */
> +static inline void *iommu_alloc_pages(gfp_t gfp, int order)
> +{
> +	struct page *page = __iommu_alloc_pages(gfp, order);
> +
> +	if (unlikely(!page))
> +		return NULL;
> +
> +	return page_address(page);
> +}
> +
> +/**
> + * iommu_alloc_page_node - allocate a zeroed page at specific NUMA node.
> + * @nid: memory NUMA node id
> + * @gfp: buddy allocator flags
> + *
> + * returns the virtual address of the allocated page
> + */
> +static inline void *iommu_alloc_page_node(int nid, gfp_t gfp)
> +{
> +	return iommu_alloc_pages_node(nid, gfp, 0);
> +}

TBH I'm not entirely convinced that saving 4 characters per invocation 
times 11 invocations makes this wrapper worthwhile :/

> +
> +/**
> + * iommu_alloc_page - allocate a zeroed page
> + * @gfp: buddy allocator flags
> + *
> + * returns the virtual address of the allocated page
> + */
> +static inline void *iommu_alloc_page(gfp_t gfp)
> +{
> +	return iommu_alloc_pages(gfp, 0);
> +}
> +
> +/**
> + * iommu_free_pages - free page of a given order
> + * @virt: virtual address of the page to be freed.
> + * @order: page order
> + */
> +static inline void iommu_free_pages(void *virt, int order)
> +{
> +	if (!virt)
> +		return;
> +
> +	__iommu_free_pages(virt_to_page(virt), order);
> +}
> +
> +/**
> + * iommu_free_page - free page
> + * @virt: virtual address of the page to be freed.
> + */
> +static inline void iommu_free_page(void *virt)
> +{
> +	iommu_free_pages(virt, 0);
> +}
> +
> +/**
> + * iommu_free_pages_list - free a list of pages.
> + * @page: the head of the lru list to be freed.
> + *
> + * There are no locking requirement for these pages, as they are going to be
> + * put on a free list as soon as refcount reaches 0. Pages are put on this LRU
> + * list once they are removed from the IOMMU page tables. However, they can
> + * still be access through debugfs.
> + */
> +static inline void iommu_free_pages_list(struct list_head *page)

Nit: I'd be inclined to call this iommu_put_pages_list for consistency.

> +{
> +	while (!list_empty(page)) {
> +		struct page *p = list_entry(page->prev, struct page, lru);
> +
> +		list_del(&p->lru);
> +		put_page(p);
> +	}
> +}

I realise now you've also missed the common freelist freeing sites in 
iommu-dma.

Thanks,
Robin.

> +
> +#endif	/* __IOMMU_PAGES_H */

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